Vapor compression distillation systems are known and are typically used for the desalination of sea water and for the production of pharmaceutical grade waters in accordance with U.S. Pharmacopeia and equivalent foreign standards. Examples of such systems are shown and explained in U.S. Pat. No. 5,587,054 issued Dec. 23, 1996 and titled “Vapor Compression Distillation System” and U.S. Pat. No. 6,365,005 issued Apr. 2, 2002 and titled “Apparatus and Method For Vapor Compression Distillation”.
It is common for such vapor compression distillation systems to utilize high speed centrifugal compressors that are driven by a standard electric motor via a suitable belt or gear transmission mounted between the motor and the compressor to step-up the speed from the motor to the appropriate rotational speed for the centrifugal compressor. The high speed centrifugal compressors can provide a suitably high outlet pressure while maintaining the compressor wheel at a small enough size to allow for the compressor to be integrally mounted to the evaporator/heat exchanger of this system in order to minimize external duct work.
In some larger vapor compression distillation systems, a direct driven motor and compressor arrangement has been used that doesn't require a belt or gear transmission to provide a step-up in speed. However, the limited rotational speed of the standard motors, typically in the range of 1,450 rpm to 3,500 rpm, requires a substantially larger compressor wheel in order to develop the required pressure at the lower operating speed of the directly driven compressor wheel. In such systems, the size of the compressor wheel and its associated housing assembly prevents integration with the evaporator/heat exchanger of the system and, accordingly, duct work must be provided between the evaporator/heat exchanger for the intake and discharge fluid streams to and from the compressor.
While the above systems may be suitable for their intended purpose there is always room for improvement.